The growing popularity of e-commerce has made warehouses increasingly vital to retailing. The authors test the proposition that competition for online consumers translates into harsher work conditions inside the warehouses that make e-commerce possible. They use data from three surveys, one providing a national sample of US warehouse workers and two targeting those at Walmart and Amazon, the country’s largest retailers. In the national sample, job quality and worker well-being are lower in warehouses engaged in e- commerce than in traditional warehouses, but this relationship varies across the two firms. The negative effects are most pronounced at Amazon’s e-commerce warehouses, which emphasize speedy delivery. These same effects are less significant at Walmart’s facilities, which aim to offer low prices. Future research should explore whether firms vying for e-commerce business are likely to emulate Amazon, converging on a set of labor practices that diminish work conditions in a growing sector.